Detection thresholds were obtained for a 500-Hz tone signal added to a
masker comprised of an amplitude modulated tone centered at the signal
frequency (on-frequency masker) and an array of amplitude modulated tones
centered at 300, 700, 800, 900, 1000, and 1100 Hz (off-frequency maskers). The
on-frequency masker was a sinusoidally amplitude modulated tone, and the
off-frequency maskers were square-wave modulated tones. On- and off-frequency
modulators were either in-phase or of random phase relative to one another, and
different conditions used square wave modulators with different duty cycles
(0%--100%). The difference between thresholds obtained in the in-phase and
random phase conditions (CMRs) were as large as 12 dB, comparable to the CMRs
found with perfectly matched modulators. Thresholds in the random phase
condition did not depend on duty cycle, but for the in-phase condition the plot
of thresholds as a function of duty cycle is ``U'' shaped. The data are in
rough agreement with ``cued-listening'' models of CMR in which the detection of
the added tone is enhanced by the cue provided by the off-frequency masker
minima. [Work supported by NIH.]